The present invention relates to acoustic energy generation, and more particularly, but not exclusively, relates to the fabrication, use, and structure of devices including an array of elements to generate ultrasonic energy for tissue ablation.
Cardiac arrhythmia, and atrial fibrillation in particular, persist as common and dangerous medical aliments associated with abnormal cardiac chamber wall tissue, and are often observed in elderly patients. In patients with cardiac arrhythmia, abnormal regions of cardiac tissue do not follow the synchronous beating cycle associated with normally conductive tissue in patients with sinus rhythm. Instead, the abnormal regions of tissue aberrantly conduct to adjacent tissues, disrupting the cardiac cycle into an asynchronous rhythm. Such abnormal conduction is known to occur at various regions of the heart.
Irregular cardiac function and corresponding hemodynamic abnormalities caused by atrial fibrillation can result in stroke, heart failure, and other medical problems. Indeed, atrial fibrillation is believed to be a significant cause of cerebral stroke. Specifically, it is theorized that the hemodynamic irregularity resulting from fibrillatory wall motion precipitates thrombus formation within the atrial chamber. A thromboembolism is ultimately dislodged into the left ventricle which thereafter pumps the embolism into the cerebral circulation that can result in a stroke. Accordingly, numerous procedures for treating atrial arrhythmia have been developed, including pharmacological, surgical, and catheter ablation procedures.
Among these, the less invasive catheter-based approaches have generally been targeted to atrial segmentation with ablation catheter devices adapted to form linear or curvilinear lesions in the wall tissue which defines the atrial chambers. Other disclosed approaches provide shaped or steerable guiding sheaves for the purpose of directing tip-ablation catheters toward the posterior left atrial wall such that sequential ablations along the predetermined path of tissue may create the desired lesion. In other approaches, atrial fibrillation is addressed with an ablation device that navigates through the circulatory system to form one or more circumferential lesions in pulmonary vein tissue. Various energy delivery modalities have been disclosed for forming lesions, including use of microwave, laser, thermal conduction, ultrasound, and more commonly radio frequency energies to create conduction blocks. U.S. Pat. Nos. 6,117,101; 6,245,064 B1; 6,254,599 B1; 6,600,174 B1; 6,608,775 B2; 6,514,249 B1; and 6,527,769 B2 provide additional background information concerning various cardiac ablation devices.
Frequently, these and other approaches do not provide a desired degree of control with respect to the targeting of ablation energy on tissue. Furthermore, for ultrasonic generating devices directed to circumferential tissue ablation, the level of power needed to ablate the surrounding tissue can result in heat dissipation problems and/or fracture of ultrasound-generating elements. Thus, there is an ongoing demand for further contributions in this area of technology. Moreover, advances in this area of technology can have application in noncardiac medical treatments and/or in nonmedical procedures.